#include<fstream>
#define NMAX 5000010

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

long long sum;
int deque[NMAX], pzd[NMAX], n, i, x, p=0, u=0, k;

int main()
{
	f>>n>>k>>x;
	deque[1]=x; pzd[1]=1; p=u=1;
	for (i=2; i<k; ++i)
	{
		f>>x;
		while (p<=u && deque[u]>x) --u;
		deque[++u]=x; pzd[u]=i;
	}
	for (i=k; i<=n; ++i)
	{
		f>>x;
		while (p<=u && deque[u]>x) --u;
		deque[++u]=x; pzd[u]=i;
		if (pzd[p]<i-k+1) ++p;
		sum+=(long long)deque[p];
	}
	g<<sum<<"\n";
	f.close();
	g.close();
	return 0;
}